Cleaning by dry ice blasting is a relatively new process that has quickly become a popular alternative to traditional cleaning methods such as steam cleaning, sandblasting, and cleaning with solvents. Dry ice blasting involves the discharge of a blasting stream substantially comprising dry ice (CO2) particles and a carrier stream of gas under pressure. The gas is usually air, although other gases such as nitrogen, carbon dioxide, or argon can also be used.
Dry ice blasting can be used to clean equipment and parts in many different industries, such as automotive, aerospace, food processing, marine and electrical industries. Dry ice blasting is particularly desirable for cleaning electrical equipment in the utilities industry, as it can provide a moistureless blasting stream, which is particularly advantageous for cleaning equipment that is sensitive to moisture. Therefore, cleaning by dry ice blasting facilitates preventative maintenance planning and avoids the potentially considerable downtimes required to clean equipment by traditional methods. Various electrical equipment can be cleaned by dry ice blasting, including pad-mounted switchgear, generator windings, transformer bushings, and substation and line insulators. The dry ice blasting stream instantly freezes contaminants on the equipment, causing the bond between the contaminants and the substrate surface of the equipment to break. The rapid velocity of the blasting stream separates the contaminants from the equipment and the dry ice quickly sublimates into a gas. As a result, there is no drying period as required in pressure washing or steam cleaning, nor is there any requirement to dispose of toxic material as required in solvent-based cleaning. Power interruptions to customers can therefore be minimized, system reliability can be improved, and the dangers associated with switching can be avoided.
Use of dry ice blasting to clean energized electrical equipment has been previously achieved. However, known dry ice blasting cleaning devices are limited to cleaning equipment energized at relatively low voltages of usually under about 50 kV, such as pad-mounted switchgear. The electric field of such low voltage equipment typically requires an operator and his cleaning device to stand at least three feet away to avoid injury, unless the cleaning device and operator are electrically insulated. Examples of such devices include electrically insulated cleaning wands that discharge CO2 through a tubular section that is thermally insulated with a polyurethane foam, thereby enabling the wand to be operated to up to around ten minutes before condensation and/or frost collects on the outer surface of the wand and degrades the electrically insulating properties of the wand beyond an acceptable safety level. Therefore, the operator must complete his cleaning task before this period, or periodically stop cleaning to allow enough time for the wand to sufficiently thaw. As such thaw periods add considerable delay to the cleaning process, operators can use multiple cleaning wands in staggered time intervals to minimize the delay.
While some low voltage electrical devices are relatively small and can be cleaned in under ten minutes, EHV electrical equipment energized to up to 500 kV are typically larger and thus take longer to clean. Furthermore, energized EHV equipment produce much larger electric fields which require a farther safe operating distance than low voltage equipment. Known dry ice blasting cleaning devices are not built with lengths or operating periods that are suitable to safely clean such energized EHV equipment.